JPS62146782A - Fail safe device for four-wheel steered vehicle - Google Patents

Abstract

PURPOSE:To prevent rear wheels from rapidly steering when a vehicle is rapidly accelerated and decelerated, by setting the limit value as a target rear wheel steering angle when the target rear wheel steering angle, determined by steering ratio and a front wheel steering angle, exceeds said rear wheel steering angle limit value determined corresponding to a car speed and acceleration. CONSTITUTION:A rear wheel steering device has a power steering device driven and controlled by a stepping motor 12, and it is controlled by a microcomputer 11. Here the microcomputer 11, which has a rear wheel steering angle determining means 31 determining a target rear wheel steering angle thetar from steering ratio (k), determined by a determining means 30 on the basis of an output of a car speed sensor 16, and an output of a front wheel steering angle sensor 15, is constituted so as to control the motor 12 in accordance with the thetar. While the microcomputer, which has a determining means 33 determining a rear wheel steering angle limit value in accordance with a car speed and acceleration, for instance, at time with the car speed larger than the steering ratio reversing car speed further with the acceleration positive, sets said limit value as the target rear wheel steering angle by a correcting means 35 when the target rear wheel steering angle exceeds said limit value.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a fail-safe device for a four-wheel steering vehicle, and relates to a four-wheel steering system configured to steer the rear wheels in an opposite phase to the front wheels at low speeds and in the same phase as the front wheels at high speeds. The present invention relates to a vehicle that prevents the rear wheels from being abruptly steered during sudden acceleration or deceleration, thereby ensuring driving safety. [Conventional technology]

2. Description of the Related Art Four-wheel steered vehicles are already known in which not only the front wheels but also the rear wheels are steered in order to achieve optimal steering performance in accordance with various situations. Among these, the one proposed and filed by the present applicant combines a stepping motor whose rotation is controlled by a control device, and a known rear wheel steering (several mechanisms) into which the rotation of this stepping motor is input. There is a device that constitutes a wheel steering device (Japanese Patent Application No. 59-25715)
No. 6). Since the amount of rotation of a stepping motor is proportional to the number of control pulses, it is easy to digitally control the stepping motor, making it easy to steer the rear wheels to the optimal steering angle set according to the vehicle speed or front wheel steering angle. Can be done. In addition, there are some models in which the rear wheels are steered by a hydraulic actuator controlled by a control device.
These also detect the front wheel steering angle and vehicle speed as control inputs, and based on these, the rear wheels are steered by a predetermined amount in a predetermined direction. By the way, in order to optimize drivability at all vehicle speeds, it is necessary to determine the rear wheel steering angle relative to the front wheel steering angle at low speeds, where centrifugal force hardly needs to be considered, and at jfh speeds, where centrifugal force needs to be considered. It is known that it is preferable to change the steering ratio k, which represents the ratio of the steering angles, as shown in FIG. 3 of the present application. Here, a region where the steering ratio k is positive indicates that the rear wheels are steered in the opposite direction to the front wheels, so-called anti-phase, and a region where the steering ratio k is negative indicates that the rear wheels are steered in the same direction as the front wheels. Indicates that the wheels are steered, that is, they are in the same phase. According to this, at low speeds, the rear wheels are steered in the opposite phase, so the center of rotation of the vehicle body moves forward and approaches the vehicle width direction line passing through the center of the vehicle body, and therefore the slip angle of the vehicle body approaches O (as well as The turning radius is smaller than when only the front wheels are steered.At high speeds, centrifugal force causes slippage between the front wheels and the road surface, which tends to shift the turning center forward. By steering the rear wheels in the same direction as the front wheels, the turning center can be brought closer to the vehicle width direction line passing through the center of the vehicle body.

[Problems to be Solved by the Invention] As shown in Figure 1, when the rear wheels are steered in opposite phases at low speeds and in the same phase at high speeds, the steering ratio k changes from positive to negative, especially in the medium speed range. has changed significantly. If we define the steering ratio k as a function only of the vehicle speed in this way and then steer the rear wheels based on this, for example, when turning suddenly and suddenly accelerating or decelerating in the medium speed range, the rear wheels will The vehicle will be steered significantly left and right, which is dangerous. This invention was devised under the above circumstances, and is applicable to a four-wheel steering vehicle in which the steering ratio k of the rear wheels is controlled to vary from the opposite phase to the same phase depending on the vehicle speed. The object of the present invention is to provide a fail-safe device that suppresses changes in the steering angle of only the first and second wheels during sudden acceleration and deceleration, thereby ensuring driving safety. [Means for Solving the Problems] In order to solve the above problems, the present invention takes the following technical measures. a front wheel steering mechanism operated by steering operation;
A front wheel steering angle sensor, a vehicle speed sensor, an acceleration detection means,
A steering ratio determining means for determining a steering ratio according to vehicle speed information from the vehicle speed sensor, the steering ratio determined by the steering ratio determining means, and front wheel steering angle information from the front wheel steering angle sensor. , comprising a target rear wheel steering angle determining means for determining a target rear wheel steering angle, and a rear wheel steering device operated by a control signal according to the target rear wheel steering angle, and at low speeds, the rear wheels are rotated in the opposite direction to the front wheels. In a four-wheel steering vehicle configured to control the rear wheels to be in the same phase as the front wheels at high speeds, the above vehicle speed condition? When the phase of the steering ratio is greater than the steering ratio reversal vehicle speed at which the steering ratio is reversed and the acceleration is positive, and when the vehicle speed information is smaller than the steering ratio reversal vehicle speed and the acceleration is negative, Rear wheel steering angle limit value determining means for determining a rear wheel steering angle limit value according to vehicle speed and acceleration, and the limit value determined by the rear wheel steering angle limit value determining means and the target rear wheel steering angle determining means. a comparison means for comparing the determined target rear wheel steering angle; and a comparison means for comparing the target rear wheel steering angle with the determined target rear wheel steering angle; The vehicle further includes rear wheel steering angle correction means.

[Operations and Effects] In the four-wheel steering vehicle of this invention, as shown in FIG. be done. therefore,
In the medium speed range, there is a steering ratio inversion vehicle speed v1 in which the phase of the steering ratio is reversed. When the vehicle speed changes from this steering ratio inversion vehicle speed V1 to the high speed side, and when the vehicle speed changes from this steering ratio reversal vehicle speed 1 to the low speed side, the absolute value of the steering ratio increases. Therefore, when rapidly accelerating from a steering ratio reversal vehicle speed ■1 and when rapidly decelerating from a steering ratio reversal vehicle speed Vl, the absolute value of the steering ratio increases rapidly, and if the front wheels are being steered significantly, this will occur. This causes the rear wheels to be abruptly steered. However, in the present invention, the rear wheel steering angle limit value determining means determines the rear wheel steering angle limit value according to the vehicle speed and acceleration at that time, and the target rear wheel steering angle is determined based on the steering ratio and the front wheel steering angle. If the angle exceeds the rear wheel steering angle limit value, this rear wheel steering angle limit value is used as the target rear wheel steering angle, so even if the steering ratio is reversed and the vehicle speed is suddenly accelerated or decelerated from 1, This makes it possible to avoid sudden steering of the rear wheels. [Description of Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. FIG. 1 is an overall configuration diagram of a four-wheel steering vehicle to which the present invention is applied. Here, a conventionally known front wheel steering mechanism 1 is used. That is, in the case of the two rank and pinion steering mechanism, the rotation of the steering shaft 3 that rotates along with the steering wheel 2 is converted into a reciprocating motion of the rack rod 5 in the gear box 4, and furthermore, this reciprocating motion of the rack rod 5 is as follows. Tyrondro at both ends, knuckle arm 7 through 6
The rotation of the knuckle arm 7.7 causes the front wheel 9.9 to move around the axis 9.
．． It is designed to be steered around 9. On the other hand, the rear wheel steering mechanism 10 includes a stepping motor 12 controlled by a control device 1) comprised of a microcomputer, and a known power steering device 14 to which the rotational output of the stepping motor 12 is input. The microcomputer 1) receives information from a front wheel steering angle sensor 15, a vehicle speed sensor 16, and an acceleration detection means 17 by differentiating the output signals of the vehicle speed sensor with respect to time as inputs for control. It has become. And this microcomputer 1)
A control line extends from the drive circuit 12a of the stepping motor 12 to the drive circuit 12a of the stepping motor 12. As the power steering device 14, for example, a known rank and pinion type power steering device can be used. That is, the control valve section 21 attached to the input section of the gear box 20 is connected to the pump 22.
Pressure oil from the input shaft 23 is sent to a double-acting power cylinder section 24 formed in the gear box 20 according to the rotational direction of the input shaft 23, and this power cylinder section 24 supports the movement of the rack rod 25. Movement of the rack rod 25 is controlled by the knuckle arms 27.26 by tie rods 26.26 connected to both ends thereof.
27, this knuckle arm 27.
8.28, thereby rotating the rear wheel 29.
29 is steered in a predetermined direction about shafts 28, 28. In the above configuration including the microcomputer 1),
The following means which can be practically realized by a program is basically configured. That is, the first one is the steering ratio determining means 30 that determines the steering ratio k according to the vehicle speed information from the vehicle speed sensor 16, and the second one is the steering ratio determining means 30 that determines the steering ratio k according to the vehicle speed information from the vehicle speed sensor 16. Then, front wheel steering angle information θf from the front wheel steering angle sensor 15
Accordingly, the rear wheel steering angle determining means 31 determines the target rear wheel steering angle θr, the third one determines the amount and direction to rotate the stepping motor 12 according to the target rear wheel steering angle,
and a pulse sending means 32 for sending a control pulse signal based on this to the drive circuit 12a of the stepping motor 12;
Fourth, when the vehicle speed information is greater than the steering ratio reversal vehicle speed ■1 at which the phase of the steering ratio is reversed, and the acceleration α detected by the acceleration sensor 17 is positive;
When the vehicle speed information is smaller than the steering ratio reversal vehicle speed ■1 and the acceleration α is negative, the rear wheel steering angle limit value that determines the rear wheel steering angle limit value θ ``− according to the vehicle speed V and acceleration α The fifth determining means 33 compares the limit value θr determined by the rear wheel steering angle limit value determining means 33 and the target rear wheel steering angle θr determined by the target rear wheel steering angle determining means 31. A sixth one is a comparison means 34 for comparing the target rear wheel steering angle θr with the rear wheel steering angle limit value θr.
The target rear wheel steering angle correction means 35 sets the above-mentioned limit values θ, Q as the target rear wheel steering angle θr when the value exceeds the target rear wheel steering angle θr. The steering ratio determining means 30 includes a data table 36 representing the relationship between the vehicle speed V and the steering ratio, as shown in FIG. The meaning of this data table 36 is as already described. Note that the intersection with the horizontal axis of the graph is the steering ratio reverse vehicle speed v1. The rear wheel steering angle limit determining means 33 also has a rear wheel steering angle limit θ corresponding to the vehicle speed V and acceleration α, as shown in FIG.
A data table 37 indicating rmu is included. In this figure, the rear wheel steering angle limit θrLl, vV1 is
It is expressed as a left and right turning angle of o. Acceleration α
The larger the absolute value of is, the more limited the rear wheel steering angle limit value is. In this figure, three stages of acceleration αl, α2 .
α3 is taken as an example to show the tendency of the corresponding rear wheel steering angle limit value, but this is merely an illustration to show the idea of the present invention, and the rear wheel steering angle limit value corresponding to each acceleration is shown steplessly. The value θr1- may be determined. The operation of the four-wheel steering vehicle equipped with the fail-safe function as described above will be further explained with reference to the schematic flowchart shown in FIG. First, the vehicle speed ■, acceleration α, and front wheel steering angle θf are read (SIOl, 102, 5103). Next, it is determined whether the absolute value of acceleration α exceeds a predetermined limit (3104), and if it exceeds (S10
4), force the rear wheels back to neutral51)2)
, and the rear wheel steering control is canceled (S1)3). this is,
More specifically, the output of the target rear wheel steering angle determining means 31 is set to 0.
Alternatively, the rack rod 25 may be forcibly returned to the neutral position by a separate actuator at the same time as the power to the stepping motor 12 is turned off. The purpose of the above steps is to detect damage to the vehicle speed sensor 16 when the acceleration value is maximized by differentiating its output information, and to stop rear wheel steering for safety. That is, unless accurate vehicle speed information is input to the microcomputer 1), the rear wheels cannot be steered to the optimum steering angle according to the data table 36. Next, the steering ratio k is determined from the vehicle speed information (2) from the vehicle speed sensor 16 and the data table 36 (S105). Next, depending on whether the vehicle speed V is larger or smaller than the steering ratio reversal vehicle speed Vl, the target rear wheel steering angle θ' is finally determined as follows.
is determined. That is, if the vehicle speed ■ is greater than the steering ratio reversal vehicle speed ■1 (YES in S106), that is, the vehicle is in a high speed state, and the acceleration α is positive (YES in S107), the vehicle speed is determined from the data table 37. And the rear wheel steering angle limit value θd- corresponding to the acceleration is read (3108). on the other hand,
In the target rear wheel steering angle determining means 35, the target rear wheel steering angle θr is determined from the above steering ratio and the front wheel steering angle θf (S
iO2), next, the rear wheel steering angle limit value θrL and the target rear wheel steering angle θr are compared 1S1)0). Here, if the target rear wheel steering angle θ' exceeds the above limit value θrm, then (
S1) '0 = YES), the above-mentioned limit value θ'- is set as the target rear wheel steering angle θr (Sill), and based on this, the amount and direction in which the stepping motor 12 should be rotated are determined, and control is performed accordingly. Pulse is stepping motor 1
(31) 7). Also,
If the acceleration α is negative in 5107 (NO in S107)
), the rear wheels are directly controlled based on the target rear wheel steering angle θr (S1) 6, 51) 7). When decelerating from a state where the vehicle speed ■ is greater than the steering ratio reversal vehicle speed Vl, as is clear from the data table 36 in FIG. This is because there is no particular problem with the above. On the other hand, if the vehicle speed V is smaller than the steering ratio reversal vehicle speed ■1 and the vehicle is decelerating (No in S I O6, 51), Y in 4.
ES), the rear wheel steering angle is determined or corrected in the same way as when accelerating at high speed (S1) 5,5
109, 5ilo, 5l1)), 51) If the acceleration α is positive in 4 (NO in S1), the rear wheels are directly controlled based on the target rear wheel steering angle θr ( 51
)6,51)7). When accelerating from a state where the vehicle speed ■ is smaller than the steering ratio reversal vehicle speed ■1, as is clear from the data table 36 in FIG. 3, the steering ratio k tends to O and the rear wheels return to neutral, so that This is because there is no problem in terms of safety. As described above, according to the present invention, in a four-wheel steering vehicle in which the rear wheels are steered in opposite phases at low speeds and in the same phase at high speeds, when sudden acceleration is performed from a vehicle speed with a reverse steering ratio, and When the steering ratio is reversed and the vehicle speed is decelerated, the danger of the rear wheels being steered significantly regardless of the driver's will is avoided, greatly increasing driving safety. Of course, the scope of the invention is not limited to the embodiments described above. For example, in the embodiment, the data table 36 is used to determine the steering ratio k corresponding to the vehicle speed ■, but this is determined by calculation by expressing the steering ratio k as a function of the vehicle speed. You may also do so. Also,
The rear wheel steering angle limit values θ and Q can also be determined by calculation. In addition, in implementation (9 (1), the acceleration detection means differentiates the acceleration α from the vehicle speed sensor with respect to time, but the signal from a single acceleration sensor can also be used as a direct control input. In the embodiment, the rear wheel steering device is configured by combining a stepping motor controlled by a control device and a power steering mechanism to which the output of this stepping motor is input. includes any mechanism controlled by a microcomputer.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram of a four-wheel steering vehicle to which the present invention is applied, Fig. 2 is a diagram showing the control system of the present invention, and Fig. 3 is a graph showing an example of the relationship between vehicle speed and steering ratio. (Data table 3
6), Figure 4 is a graph (data table 3) showing an example of the relationship between the acceleration α and the corresponding rear wheel steering angle limit θ.
7), FIG. 5 is a flowchart showing an example of the flow of control by the control device. 1... Front wheel steering mechanism, 2... Steering, 10.
... Rear wheel steering device, 15... Front wheel steering angle sensor, 16.
...Vehicle speed sensor, 17...Acceleration sensor, 30...
Steering ratio determining means, 31...Target rear wheel steering angle determining means, 3
3... Rear wheel steering angle limit value determination means, 34... Comparison means, 35... Target rear wheel steering angle correction means.

Claims (1)

[Claims] (1) A front wheel steering mechanism operated by steering operation, a front wheel steering angle sensor, a vehicle speed sensor, an acceleration detection means, and a steering ratio determination that determines a steering ratio according to vehicle speed information from the vehicle speed sensor. means, target rear wheel steering angle determining means for determining a target rear wheel steering angle based on the steering ratio determined by the steering ratio determining means and front wheel steering angle information from the front wheel steering angle sensor; It is equipped with a rear wheel steering device that is activated by a control signal according to the rear wheel steering angle, and is configured to control the rear wheels to be in the opposite phase to the front wheels at low speeds and to be in the same phase as the front wheels at high speeds. In a four-wheel steering vehicle, the above vehicle speed information is
When the phase of the steering ratio is larger than the steering ratio reversal vehicle speed and the acceleration is positive, and when the vehicle speed information is smaller than the steering ratio reversal vehicle speed and the acceleration is negative, the vehicle speed and acceleration. rear wheel steering angle limit value determining means for determining a rear wheel steering angle limit value according to the rear wheel steering angle limit value determining means, and a limit value determined by the rear wheel steering angle limit value determining means and the target rear wheel steering angle determining means. a comparison means for comparing the target rear wheel steering angle with a target rear wheel steering angle; and a target rear wheel steering angle in which the target rear wheel steering angle is set as the target rear wheel steering angle when the target rear wheel steering angle exceeds the rear wheel steering angle limit value in the comparing means. A fail-safe device for a four-wheel steering vehicle, further comprising a correction means.